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Aromaticity in heterocyclic systems III. The structure and proton magnetic resonance spectra of certain imidazo[1,2‐a]pyridines
Author(s) -
Paolini John P.,
Robins Roland K.
Publication year - 1965
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570020110
Subject(s) - chemistry , pyridine , tautomer , proton magnetic resonance , yield (engineering) , proton , proton nmr , spectral line , resonance (particle physics) , 2 pyridone , medicinal chemistry , stereochemistry , nuclear magnetic resonance , physics , materials science , quantum mechanics , astronomy , particle physics , metallurgy
A number of improved laboratory procedures for the synthesis of derivatives ofimidazo‐[1,2‐alpyridines are reported. These methods have been employed for the preparation of 5‐chloroimidazo[1,2‐alpyridine (IX), 5‐aminoimidazo[1,2‐a]pyridine (IV), 2‐methyl and 2,3‐dimethyl‐5‐aminoimidazo[1,2‐a]pyridine. The proton magnetic resonance spectra of imidazo[1,2‐a]pyridine (I) have been studied and the bands assigned by a comparison of spectral patterns of simple derivatives. The proton magnetic resonance spectra were then utilized to assign predominant tautomeric structures to imidazo[1, 2‐a]‐2‐pyridone (IIIb), imidazo[1,2‐a]‐(1H)‐5‐pyridone (VIIb) and 5‐aminoimidazo‐[1, 2‐alpyridine (IV). The synthesis of imidazo[1,2‐a]‐(1H)‐5‐pyridone (VII) was accomplished from 5‐chloro‐imidazo[1, 2‐alpyridine (IX) via 5‐benzyloximidazo[1,2‐a]pyridine (X) which was debeneylated catalytically to yield VII. Bromoacetaldehyde and 2‐amino‐4‐chloropyridine gave 7‐chloroimidazo[1,2‐a]pyridine.